Scoping a double generally alters barrels harmonics and a choice has to be made :

1. zero in the scope with 1 bbl. (= single-shot) ;
2. have the bbls. regulated with scope on, knowing they won't shoot the same afterwards without scope.

When I had my FN o/u 9,3x74R scoped, I chose the Swarovski 1,25-4x24, had the bbls. re-regulated (they now shoot in 1 hole at 50 m) and use it on 2x for close shots at running game.